INTERVIEW: Multiple challenges face land subsidence problem

New Public Construction Commission (PCC) Minister Lee Hong-yuan recently sat down with ‘Taipei Times’ staff reporter Tzou Jiing-wen to share his views on the issue of land subsidence facing Taiwan High Speed Rail in areas around Changhua, Yunlin and Chiayi. The only way to resolve the problem is to change the water intake structure, he said, adding there was a need for inter-agency dialogue

Public Construction Commission Minister Lee Hong-yuan gestures in a photo on April 15.

Photo: Fang Pin-chao, Taipei Times

Taipei Times: The land subsidence issue in the Changhua, Yunlin and Chiayi areas is endangering Taiwan High Speed Rail. How serious is the situation?

Lee Hong-yuan (李鴻源): The land subsidence areas in Changhua, Yunlin and Chiayi occupy about 1,200km2, which is one-tenth the size of the western plains of Taiwan. Some of the severe land subsidence areas have dropped to 3m below ground level or even lower. In the past, it was the consequence of excessive groundwater pumping. Everyone blamed the fish-farming industry for it, but in actuality, all water use — including industrial use and tap water — has been provided through excessive groundwater pumping. And why is it so? Because there isn’t any reliable source of surface water available.

There is a myth that says once the Hushan Reservoir (湖山水庫) in Yunlin County is constructed, the land subsidence problem will be solved, but this is not true. The water-holding capacity of Hushan Reservoir is about 50 million tonnes and can only be used four times a year at most, supplying 200 million tonnes of surface water. However, the Changhua, Yunlin and Chiayi areas extract between 500 million and 600 million tonnes of groundwater every year. It’s out of proportion. The bad news now is that land subsidence is gradually moving inland, whereas in the past it only occurred in the coastal areas. Even worse is that the more severe areas happen to be where the high-speed rail passes through. Although the speed of land sinking varies every year — about 7cm on average — it seriously impacts the safety and maintenance of the high-speed rail.

The high-speed rail is constructed where the water usage structure is very unbalanced. Constructing reinforcements is only a temporary solution. If groundwater extraction continues without changing the water-use structure, the reinforcement measures will lose effect in two to four years. The problem at hand is tricky.

TT: What is the permanent solution?

Lee: As a professor at National Taiwan University four years ago, I helped the Water Resources Agency [WRA] plan a comprehensive water governance and management plan for Dongshih (東石), Budai (布袋) and Yijhu (義竹), in Chiayi County. The first thing we did was communicate to fishermen and fish farmers that they shouldn’t pump groundwater. They refused at first, but after many hours of explaining, some of them took our advice, or at least were no longer opposed to it.

You need to understand their problems and solve them. They make a living by using groundwater, but how can it be balanced with water governance and management? I think it’s important to bring these issues back to a professional level, telling them that if groundwater pumping continues, their houses will sink below ground level and become worthless then. Moreover, we asked them to think about how much it would cost to raise their house every four years, how much they would lose if it flooded or if a typhoon destroyed the fish farms.

Afterward, I asked them what assistance they needed from the government and in a scenario where government expropriation is impossible, would they be willing to rent their fish farm to the government, or would they be willing to cooperate with farmland and wetland readjustments to turn their fish farms into flood detention pond-constructed wetlands?